363
FXUS63 KLOT 300606
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
106 AM CDT Tue Apr 30 2024

.KEY MESSAGES...

- Chance (30%) of showers through sunset.

- After a break on Tuesday, a stormy pattern returns for a
  period midweek along with continued unseasonably warm
  temperatures.

&&

.DISCUSSION...
Issued at 252 PM CDT Mon Apr 29 2024

Through Tuesday Night:

A cold front will move across the area late this afternoon into
early this evening with a chance of showers through sunset,
ending from west to east with the cold front. Instability is
weak but an isolated thunderstorm is possible generally east of
I-57. Southwest winds will slowly turn westerly and remain gusty
to 30 mph through sunset and then will quickly diminish.

Quiet and dry weather is expected tonight and Tuesday. Lows in
the 40s for most areas tonight, lower 50s in Chicago. Highs will
rebound well into the 70s for Tuesday with a lake breeze
expected, which will likely move inland in the late afternoon
and early evening before dissipating, turning temps cooler
behind it.

Another cold front will move across the area Tuesday night.
Convection is expected to develop Tuesday afternoon well west of
the local area and spread into the area in the late evening and
overnight but in a weakening/dissipating phase. Much of the
guidance keeps the eastern half of the area completely dry now.
Lowered pops for Tuesday night and if current trends continue,
much of the area may remain dry. cms

Wednesday through Monday:

Dry and mild weather is expected for Wednesday, with high
temperatures expected to be in the 70s. However, cooler
conditions are likely to develop along the Lake Michigan shores
late in the day as the winds will turn east-northeasterly with
the approach of backdoor cold front. This cold front will
ultimately shift back northward across far northern IL into
southern WI as a warm front on Thursday in response to the next
wave of low pressure tracking northeastward into the Upper
Midwest. As this occurs, increasing warm air advection over the
front may foster the development of scatted elevated showers and
storms over parts of northern IL late Wednesday night into
Thursday morning. The focus for these storms should then shift
northward into WI with the warm front into Thursday afternoon,
thus leaving our area in the breezy warm sector. Breezy south
winds (gusting 30 to 35 mph) Thursday afternoon could push
temperatures into the lower to mid 80s for highs.

The parent surface low is expected to occlude late Thursday
night as it shifts northward into northern MN and far
southwestern Ontario. As it does so, the attendant surface cold
front will slide eastward into our area late Thursday night into
Friday. An additional period of showers and thunderstorms is
likely to accompany this front, with the highest chances (60%+
chances) coming Thursday night through Friday morning. We will
need to continue to monitor the potential for any hydrologic
concerns during this time frame given the recent rainfall and
that precipitable water values near or in excess of 1.5" (near-
record values for this time of year here, per DVN and ILX
sounding climatology) are progged to be drawn northward out
ahead of the cold front. A north-northeastward storm movement
could also result in a period of training cells along the cold
frontal boundary, which may lead to some narrow corridors of
enhanced rainfall and possible flooding.

In the wake of the cold frontal passage, temperatures are
favored to return closer to normal going into the weekend before
another warm-up appears to be on the horizon going into next week.

KJB

&&

.AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 106 AM CDT Tue Apr 30 2024

Key Messages:

- Southeasterly wind shift expected late this afternoon/early
  this evening at the Chicago metro TAF sites

- Chance of showers late Tuesday night

Mostly clear skies and westerly winds to around 10 kts are
expected through this afternoon. A lake breeze will develop
this afternoon, but will likely remain tethered to the Lake
Michigan shoreline for most of its lifespan. It may begin to
progress inland late this afternoon/early this evening, but will
probably start to wash out before reaching ORD and MDW. However,
even if this happens, a synoptically-driven southeasterly wind
shift appears to be likely for a few hours this evening before
winds gradually start to trend back towards a southwesterly
direction.

A decaying convective complex coming out of Iowa is likely to
survive into northern Illinois late Tuesday night, but the
extent to which it may affect the terminals is still in question.
For now, have added a PROB30 mention for -SHRA to account for
this and will reassess again later. A few lightning strikes can`t
entirely be ruled out if this complex doesn`t weaken as quickly
as presently expected, but the probability of this occurring is
currently too low to warrant including a TSRA or VCTS mention
in the TAFs. The best chances to see any rain or lightning
should be at RFD. Some lower (potentially sub-VFR) cloud cover
may also accompany this activity and linger around into
Wednesday morning, but confidence in this currently low.

Lastly, there is also some potential for low-level wind shear
criteria to be breached Tuesday night into Wednesday morning.
However, winds at the surface look to remain elevated enough
during this time frame to preclude the need for a formal LLWS
mention in the TAFs.

Ogorek

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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